How can I prevent my text object from flickering?
The problem seems to be because of your camera's clipping options.


You have these starting from 1mm and continuing to 10km, while limits closer to the actual visible range of your scene would be more sensible.

I'm cutting some corners about the actual math involved, but basically the way these settings work, is that the range you have set is divided into different distance steps to the camera, within possible computing precision, when determining what things are in front or behind other things. There is limited precision in this rendering code for this distance information, so bigger range for the camera clipping means bigger steps in comparing distances, so objects with only a small distance between them might end up in the same distance step and go in the wrong order.

Having smaller clipping range makes also these steps smaller, so the rendering code is able to differentiate between smaller distances as well. Note that there's a lot more of this precision near the "near" plane than near the "far" plane, so increasing the "Start" value might have even more impact than reducing the "End" value, even if the amount you change it is far less.

A range from 1m to 300m or so would be ok for your scene.